Want to see a micromachined marvel in action? Look inside an ink-jet printer. The basic guts are mechanical: a stepper motor turns a belt that moves the print head assembly back and forth across the target page. The assembly holds the ink cartridges. Instructions on what to print are sent through a wire ribbon that bends with the moving assembly. But that's where the microscopic world takes charge.

Piezoelectric printers (Epson) have a permanent print head in the assembly; the cartridge just supplies ink. The head charges vibrating crystals that push ink droplets out tiny nozzles. In thermal ink-jet, or "bubble-jet," printers (Canon, Hewlett-Packard) the print head is inside the ink cartridge, which includes all the microtechnology and an integrated circuit--quite a feat for $20. The head superheats ink so an exploding vapor bubble jettisons a droplet through a nozzle. In either design, the print head may contain 360 to 600 jets in less than a square inch. Each jet is fed by its own ink channel and is triggered many times a second by its own resistor or crystal. "Everyone talks about MEMS [microelectromechanical systems] these days," observes Frank L. Cloutier, chief technology officer at Hewlett-Packard's Imaging and Printing Group in Corvallis, Ore. "This is MEMS, and we've been doing it for 18 years."

This article was originally published with the title Superhot Dots.

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